Sandy Rea, psychologist and relationship expert on relationship TV show The Last Resort explains it best. She says, "Resentment is a bit like swallowing a poison pill and expecting someone else to die. You end up poisoning yourself by taking this pill. It has no impact on the other person."

That's why most couples have the same fights over and over and over again.

That's why issues of the past continue to haunt couples for years, if not decades.

That's why once there's betrayal, rejection, hurt or mistrust it can be so hard to stay together.

Hard, but not impossible.

The relationship expert explains that while it's easy for couples to become "stuck" in a cycle of resentment, as long as there is love, there's hope.

You just have to look at the five couples on The Last Resort and how stuck each of them is in their own individual issues, but despite the different causes of they resentment they are feeling, they still all have one thing in common.

Resentment towards each other and associated unhelpful behaviours triggered by it.

(The Last Resort, Nine)

Jodie feels resentful that she's in a sexless marriage with Stu. Image: The Last Resort, Nine

Five very different couples with a variety of issues but at the heart of their problems is the lingering blame, hurt and anger.

Sandy says if you suspect your relationship may be stuck in its own cycle of resentment, there's a very easy way to identify it. "If you have an issue that keeps recurring - you don't understand me, you don't listen to me - they're the sorts of very obvious clues that people are holding onto resentment."

The biggest reason couples become stuck in resentment, she says, is because either one or both partners is stubbornly holding onto their position.

“When you hold onto resentment you’re pretty much saying, ‘I am immovable," she explains. "This is the position that I am going to take. I am not giving that position up.’ And that validates you. It says, ‘We take no blame’.”

And the reason for posturing - the repeating of grievances and the revisiting of blame - is because someone feels they are not being heard or understood.

"The reason you continue to posture on a certain point is because you're not being listened to, you're not being heard," Sandy Rea says. "The other person is not understanding your position and until you get that empathy, it's really critical when it comes to resentment and learning forgiveness."

(The Last Resort, Nine)

Sharday and Josh are separated and are trapped in a cycle of hurt and blame. Image: The Last Resort, Nine

Psychologist Sandy Rea recommends the following steps for couples who feel as though they are stuck in a cycle of resentment:

1. Empathy

Try and put yourself in your partner's shoes.

2. Listen

When your partner truly comprehends the damage that their behaviour has caused someone, that's when healing begins.

3. Identify

Every relationship has really bad habits and in psychological terms we call that when you’re ‘stuck’. And when you’re stuck you get into a repetitive cycle of bad habits. It’s as simple as that. They don’t have the resources, the strategy, the alternative to change those bad habits which is often why they come into therapy.

4. Choice

There is a choice. Behaviour can change but the reason that some behaviours change or don’t change is, we call it you need to be ‘treatment ready’. They just aren’t prepared to do what is needed to do to practice new behaviours and change those bad habits.

5. Change

Change is difficult. It’s confronting. It means that you have to jump off that pedestal of moral superiority. That’s what it means. It means you have developed empathy towards your partner’s position and you may not want to have that empathy.

By not trying to change, “what you are saying is, ‘I am right, you are wrong and I’m going to preserve this image of myself, whatever the actual behavior is’.” So it gives you all of that moral superiority. It means that you don’t have to change.”

6. Help

There are different choices, there are different ways of behaving.

Watch The Last Resort on Tuesday and Wednesday nights at 7.30 on Channel 9, or catch up on 9 Now.